The present invention relates to laminated gaskets used for providing seals, for example, between the opposed surfaces of the cylinder block and cylinder head of an engine.
For sealing the joint between the opposed surfaces of the cylinder block and cylinder head of an engine, there have been widely used gaskets composed of elastic metal plates. Such laminated gaskets are often designed such that elastic metal plates having beads or folded-back portions are laminated to another structural plate in order to enhance a sealing effect particularly in the areas around the peripheries of bore openings.
For producing lightweight and small-sized engines, there are two concurrent noticeable tendencies in the recent development of engines. One is a trend toward making all of the structural members of an engine from aluminum alloys and the other is a trend toward higher combustion pressure for seeking higher output, higher performance engines. Although more lightweight cylinder heads and cylinder blocks etc. can be produced from aluminum alloys, compared to cases where iron materials are used, the use of aluminum alloys disadvantageously provides poor rigidity which causes considerable deformation in the cylinder head and the cylinder block when clamping the cylinder head gasket, so that it becomes difficult to obtain uniform static sealing surface pressure around the peripheries of the bore openings. In addition, during an operation of the engine, the relative displacement of the cylinder head and the cylinder block is increased by high pressure within the cylinders and heat, which leads to difficulty in achieving uniform dynamic sealing surface pressure.
To solve this problem, the following cylinder head gaskets have been proposed and put to practical use, which have structures of high freedom to conform to slips and deformation occurring around the peripheries of the bore openings.
(1) Japanese Patent Publication (KOKAI) No. 63-101575 (1988)
This publication discloses a gasket having a structure in which a plate, which has beads and folded-back portions including comparatively large clearances, is overlaid on another structural plate.
(2) Japanese Utility Model Publication (KOKAI) No. 1-118147 (1989)
This publication discloses a gasket having a structure in which a plate has folded-back portions having xcex1-shaped clearances around a bore opening and a bead, and another plate is placed so as not to overlap with the folded-back portions.
(3) Japanese Utility Model Publication (KOKAI) No. 4-66457 (1992), Japanese Patent Publication (KOKAI) No. 5-52268 (1993)
These publications disclose a gasket having a four-plate-structure in which a first intermediate plate having folded-back stoppers and a second intermediate plate having step-like stoppers are sandwiched between two bead plates. The folded-back stoppers for preventing entire bead compression are formed only on a side of either of the bead plates.
(4) Japanese Patent Publication (KOKAI) No. 10-61773 (1998)
This publication discloses a structure in which bead plates are laminated to both sides of an intermediate plate and thickness increasing stopper portions made from a sintered material are formed on the bead plates.
These conventional gaskets have, however, revealed the following disadvantages. The gasket of column (1) has a problem in its conformability to the deformation of the cylinder head and cylinder block since the comparatively large clearance formed in the folded-back portion is a grommet-like folded portion. Neither of the gaskets described in columns (1) and (2) have an outer laminated plate which directly contacts the folded-back portions and they are in the form of a single layer at the parts around the bore openings so that it is difficult to keep springiness and therefore a surface pressure adjustment for bore sealing cannot be easily performed.
In the gasket of the four-plate-structure described in column (3), the distortion of the second intermediate plate having the step-like stopper is virtually unexpected and the absence of the distortion causes no problem in the performance of the gasket. Therefore, virtually no effect of the folded-back stopper formed on one side is transmitted through the thick, second intermediate plate to the cylinder head surface or the cylinder block surface on the opposite side. In case where the folded-back stopper is positioned toward the cylinder block side, as a whole the gasket when tightening and in use cannot follow the deformation occurring on the cylinder head, or vice versa. It becomes therefore difficult to simultaneously maintain desired sealing surface pressures on the cylinder head side and on the cylinder block side. It should be noted herein that where the cylinder block is made of cast iron whereas the cylinder head is made of an aluminum alloy, deformation can be dealt with in some degree which may be somehow insufficient though, by appropriately adjusting the orientation of the gasket of the four-plate-structure. However, the problems described above are dominant in the case of engines entirely made of aluminum alloys such as the latest open deck type engines.
In the gasket described in column (4), since the thickness increasing stopper is made of a sintered material, increased costs due to the material and the sintering process are unavoidable.
The invention has been directed to overcoming the foregoing problems and it is therefore a prime object of the invention to provide a laminated gasket of a comparatively simple structure, in which desired bore sealing surface pressures on both of the cylinder head side and the cylinder block side can be ensured by use of elastic plates having at least folded-back portions formed so as to follow the deformations of the cylinder head and the cylinder block and in which excellent sealing ability and durability can be achieved preferably by a double sealing function.
The above object can be achieved by a laminated gasket constructed according to a first aspect of the invention, which has a core plate and elastic plates laminated to both surfaces of the core plate,
wherein the core plate has thin-walled portions each of which surrounds a bore opening and a thick-walled portion extending outwardly from the thin-walled portions, and
wherein each of the elastic plates has (a) folded-back portions each of which is formed so as to create, together with a base portion, a clearance around its associated bore opening and (b) beads each of which is formed outside its associated folded-back portion.
According to the invention, since the folded-back portions formed on the elastic plates are each formed so as to create a clearance together with a base portion, the clearances can remain as much as possible when the elastic plates are tightened between the opposed surfaces of the cylinder head and the cylinder block, so that bore seal lines can be formed by these folded-back portions. In addition, a double seal structure composed of a first seal provided by the folded-back portions formed on the elastic plates and a second seal provided by the beads can be achieved and thus, good sealing effects can be achieved with a relatively simple structure. Since the thin-walled portions of the core plate allow the folded-back portions having a clearance and formed on the elastic plates to maintain springiness, the gasket can conform to the deformation of the cylinder head or cylinder block when the gasket is tightened or when the engine is operated. Additionally, since the elastic plate is provided for both surfaces of the core plate, even if deformation occurs from both of the cylinder head side and the cylinder block side when the gasket is tightened, the elastic plates flexibly receive the stresses so that surface pressures on both sides can be distributed as desired. Further, the gasket can easily follow the deformation of the cylinder head or the cylinder block, exerting good sealing effects, during an operation of the engine. Accordingly, a gasket having excellent sealing ability and durability can be achieved.
The gasket of the invention may be structured such that each of the thin-walled portions is an inclined thin-walled portion which gradually becomes thinner toward its associated bore opening and such that the folded-back portions and beads of the elastic plates are in contact with their associated inclined thin-walled portion. In such a structure, the folded-back portions of the elastic plates can be allowed to maintain springiness by the inclined thin-walled portions of the core plate when the gasket is tightened or the engine is operated.
Alternatively, the gasket of the invention may be structured such that each of the thin-walled portions is a step-like thin-walled portion which is formed by thinning a part on the side of each bore opening and such that the folded-back portions of the elastic plates are in contact with their associated step-like thin-walled portion whereas the beads of the elastic plates are in contact with the thick-walled portion.
According to a second aspect of the invention, there is provided a laminated gasket which has a core plate and elastic plates laminated to both surfaces of the core plate,
wherein the core plate has thin-walled portions each of which surrounds a bore opening and a thick-walled portion extending outwardly from the thin-walled portions, and
wherein each of the elastic plates has (a) folded-back portions each of which is formed so as to create, together with a base portion, a clearance around its associated bore opening and (b) seal portions each of which is made of a soft sealing material and positioned outside its associated folded-back portion.
According to the invention, a double seal structure can be achieved, which is composed of a first seal provided by the folded-back portions formed on the elastic plates and a second seal provided by the seal portions formed outside the folded-back portions. With this arrangement, the same effect as obtained by the first aspect can be achieved.
The invention may be arranged such that each of the thin-walled portions is an inclined thin-walled portion which gradually becomes thinner toward its associated bore opening and such that the folded-back portions of the elastic plates are in contact with their associated inclined thin-walled portion.
The invention may be alternatively arranged such that each of the thin-walled portions is a step-like thin-walled portion which is formed by thinning a part on the side of each bore opening and such that the folded-back portions of the elastic plates are in contact with their associated step-like thin-walled portion.
According to a third aspect of the invention, there is provided a laminated gasket which has a core plate and elastic plates laminated to both surfaces of the core plate,
wherein the core plate has (a) thin-walled portions each of which surrounds a bore opening, (b) a thick-walled portion extending outwardly from the thin-walled portions and (c) seal portions made of a soft sealing material and formed on the thin-walled portions and/or the thick-walled portion,
wherein each of the elastic plates has folded-back portions each of which is formed so as to create, together with a base portion, a clearance around its associated bore opening.
According to the invention, a double seal structure can be achieved, which is composed of a first seal provided by the folded-back portions formed on the elastic plates and a second seal provided by the seal portions formed on the thin and/or thick-walled portion of the core plate. With this arrangement, the same effect as obtained by the first aspect can be achieved.
The invention may be arranged such that each of the thin-walled portions is an inclined thin-walled portion which gradually becomes thinner toward its associated bore opening and such that the folded-back portions of the elastic plates are in contact with their associated inclined thin-walled portion.
The invention may be alternatively arranged such that each of the thin-walled portions is a step-like thin-walled portion which is formed by thinning a part on the side of each bore opening, such that the folded-back portions of the elastic plate are in contact with their associated step-like thin-walled portion, and such that the radial length of the base portions of the elastic plates is within the range equal to the radial length of the step-like thin-walled portions and the elastic plates are not in contact with the thick-walled portion of the core plate. This arrangement provides a much simpler structure in which no elastic plates are laminated to the thick-walled portion of the core plate.
Another alternative arrangement is such that each of the thin-walled portions is a step-like thin-walled portion which is formed by thinning a part on the side of each bore opening, such that the folded-back portions of each elastic plate are in contact with their associated step-like thin-walled portion, and such that the base portion of each elastic plate holds an end of the step-like thin-walled portion and the elastic plates are not in contact with the thick-walled portion of the core plate. Similarly to the above arrangements, this arrangement provides a much simpler structure.